World Ocean Day is an opportunity every year to honour the world's ocean, celebrate the products the ocean provides, such as seafood, as well as marine life itself for aquariums, pets, and also a time to appreciate its own intrinsic value.

The world's oceans cover more than 70% of our planet's surface. Among other things they provide us with food and a place to play. On the ocean bed there are mountains, valleys and even volcanoes.

How many Oceans are there in the world?

Most of the world's water is contained in its five* oceans - the Pacific, Atlantic, Indian, Arctic and Southern (Antarctica).

*For many years only four oceans were officially recognised, and then in the spring of 2000, the International Hydrographic Organization established the Southern Ocean.

The Pacific Ocean (155,557,000 sq km)

The Pacific Ocean is the largest and deepest ocean in the world. The Pacific Ocean is so big it could fit all of the Earth’s continents. The deepest known spot in the ocean is the Mariana Trench, southwest of Guam, it is 11,033 metres below the surface (36, 198 feet). Thousands of volcanoes rise up from the Pacific Ocean.

The Atlantic Ocean (76,762,000 sq km)

The Atlantic Ocean is the second largest body of water. The deepest part of the Atlantic Ocean is the Puerto Rico Trench 28, 374 feet (8,648 meters).

The Indian Ocean (68,556,000 sq km)

The Southern Ocean (Antarctica) (20,327,000 sq km)

The Arctic Ocean (14,056,000 sq km)

The Arctic Ocean lies at the top of the world and is the smallest ocean, holding only one percent of the Earth's seawater. Most of the Arctic is frozen and covered in ice. During the summer some of the ice melts, releasing huge blocks of drifting ice called pack ice or smaller chunks called icebergs. The Arctic Ocean covers about 3,662,000 square miles (9,485,100 square kilometres). Its greatest depth is 17,880 feet (5,450 metres).

Why are oceans and seas salty?

Salt in the oceans and seas comes from rocks that have been eroded (broken and worn down) by the wind and water. Chemicals from the rocks dissolve in the water and make it salty.

What causes the tides?

Tides are caused by gravity, or the pull of the Earth towards the moon. The force of gravity pulls the oceans towards the direction of the moon.

What causes waves?

Waves on the surface of the oceans are caused by the energy of the wind.
Tsunamis however, are caused by underwater earthquakes or volcanoes.

Facts about oceans

• More than 97% of all our planet's water is contained in the ocean
• The average depth of the ocean is more than 2.5 miles
• Mount Everest (the highest point on the Earth's surface 5.49 miles) is more than 1 mile shorter than the Challenger Deep (the deepest point in the ocean at 6.86 miles)
• The underwater mountain range known as the Mid-Ocean Ridge stretches 74,000 km, which is 4 times the length of the Andes, Rockies and Himalayas combined.
• The Monterey Bay Submarine Canyon is deeper and larger in volume than the Grand Canyon
• The average temperature of the oceans is 2ºC (about 39ºF)
• The blue whale, the largest animal on our planet ever still lives in the ocean; it's heart is the size of a Volkswagen
• The Great Barrier Reef, measuring 1,243 miles, is the largest living structure on Earth. It can be seen from the Moon.
• Plastic waste kills up to 1 million sea birds, 100,000 sea mammals and countless fish each year. Plastic remains in our ecosystem for years harming thousands of sea creatures everyday.
• Over the past decade, an average of 600,000 barrels of oil a year has been accidentally spilled from ships, the equivalent of 12 disasters the size of the sinking of the oil tanker Prestige in 2002.

World Ocean Day on the web
www.theoceanproject.org/wod/